Two of us at work use iTunes, and could see each others' shared libraries in our iTunes browser. However, when we tried to open each others' libraries, we were unable to do so. Clicking on my colleague's library caused the info panel to show it was trying to connect, but then iTunes flipped back to my library.
We found that this is because we use a proxy server for internet connections, and neither of us had the 'Bypass proxy settings' set for our local domains. Adding our domains solved the problem.

